Cambrian and Ordovician Periods lecture notes.doc

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24 Mar 2012
Cambrian and Ordovician Periods
Slide 1:
Cambrian Period
-540 million years ago
-beginnings of multicellular life
-stem from 3 lineages of organisms
-explosion in diversity of multicellular forms
-many organisms are found in the shell deposits
-laurentia (plate in which North America ultimately emerges) surrounded by continental
-shallow water, lots of sunlight, warm = primary productivity
Slide 2:
-fossils contain soft-bodied animals / invertebrates
-Yoho National Park and the Burgess Shales
-contains sets of animals that have never been seen again
Slide 5:
-animals from Burgess Shales bear little resemblance to animals today
-when multicellular life arose, it was at its most diverse and complex when it first occurred;
the amount of complexity has been diminishing over time
-contrasts idea that diversity increases and Darwin's idea of slow gradual change
-30 animal body plans appear in the Burgess Shales and some still exist today
-2 new morphologies
-burrowing animals
-animals that swim and chase their pray
Slide 7:
-phylogeny starts from colonial cells (choanoflagellate cells) (origins of animals)
-cell that has a cell body and flagellum and a microcollar surrounding body
Slide 13:
-choanoflagellate cells
-origins of animals; ancestral cell to all organisms
-cell that has a cell body and flagellum (1) and a microvilli that forms a collar
surrounding the flagellum at the centre
-cell feeds (as a single cell protist) by pumping water (movement of the flagellum
brings water into the microvilli and propels it away)
-water contains small photosynthetic algae (primary photosynthetic organisms of
the ocean) and become trapped as particulate material which is then consumed by
-develops symmetry (circular / radial or bilateral)
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Slide 9:
Origins of Tissues
-either single cells, cells working as a colony, cells working together as tissue, or you don't
have tissue but have a group of cells that have different functions = multicellularity
-if there are no tissues but have cells that do different tasks = multicellularity
-cells working together with a communication system between groups of cells
-different function in cells (specialized function)
-many cells
ectoderm- epidermal layer that surrounds organism
endoderm- epidermal layer that surrounds digestive tract
mesoderm- primarily muscle tissue
diploblastic - ectoderm and endoderm (found in the simplest of organisms)
triploblastic- ectoderm, endoderm, and mesoderm (allows for complexity)
-the earliest divisions in phylogeny
Slide 11:
-no tissues -> sponges (porifera)
-most ancestral and simple of all organisms; the first animal
-takes choanocytes and organizes them into a sheet inside a hollow structure
-hollow centre with wall that has choanocytes lining the inside
-outside is epidermal like layer
-pumps water through openings in the walls and pushes it through the top for water
-as water passes by choanocytes, it traps food particles and consumes it by
-outside is pinacocytes
-pinacoderm made of pinacocytes -> outer layer that allows water to move in to trap food
-different cell types with different functions make sponges multicellular
-amoebocytes travel around to feed pinacocytes in the sponges (food movement)
-sponges have skeleton of minerals (minerals secreted by cells which also get food from
-cells stuck together by collagen (a defining characteristic of animals)
-uses mineralized calcium or silica for skeleton
-calcium cannot be used in deep oceans due to pressure
-most effective filters of ocean water; process the largest amount of water and captures
primary productivity
Slide 12:
Sponge Reproduction
-choanocyte (with flagellum) morphs to sperm (due to swimming structure)
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-beating causes a current and releases sperm
-"smoking" release of sperm
-another sponge (archeocyte / amoebocyte) filters water and traps particles of
sperm on microvilli; sponge recognizes sperm of its own species and passes it to
an amoebocyte and the egg is fertilized, producing a zygote)
Slide 14:
-symmetry tells us about the lifestyle / mode of living associated with the organism and
these 2 types of symmetry involve organisms that have tissue
Radial Symmetry
-symmetry based upon oral opening and its opposite end (aboral side)
-if you slice through the organism (oral to aboral side), the halves are identical and this can
be done in more than one plane around the surface of the animal
-ideal for something that is sessile (immobile); if it is anchored in place, it has to monitor
all directions around it
-ideal for passively floating organisms as well
-simple nervous systems
-diploblastic organisms
-i.e.: cnidaria (corals, jellyfish)
Bilateral Symmetry
-organism is using locomotary skills to move and it has a directed motion; therefore it
needs to get sensory information from the direction where you're going
-concentration of sensory information at anterior / forward leading end of the organism
-it picks up information about where its going
-if you're trying to escape from predators, you need to know where you need to go
-applies to food and mating as well
-from the oral to aboral end, there is only 1 plane that you can divide in half in order to get
equal halves (i.e.: humans)
-when this comes along, we get active animals that are capable to do many things in the
-triploblastic organisms; mesoderm needed for movement which is characteristic of
bilaterally symmetric organisms
-sponges have no symmetry since they have no oral or aboral ends
Slide 16:
-made up of cnidarian
-live in colonies which are capable of producing the coral reefs which begin during the
-polyps that live inside a calcareous (calcium carbonate) skeleton grow and divide and
form coral reefs
-coral reefs create the most biodiverse habitat in a marine environment
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